Barometric installation

Space constraint Require elevated platforms for surface condensers, (semi-) barometric drain pipes for condensate removal, and separators for separating foul water and oil. Non-barometric installation is possible by combining SJEs and LRVPs Surface condensers and elevated structures are not required. Instead, they require closed-loop liquid coolers for reducing water consumption and gas-liquid-liquid separators. They are compact and require less plot space... 

A very common layout for the assembly of condensers is barometric installation, the method in which no pump is needed to extract the liquid from under vacuum. The condenser is erected at such a height above the liquid drain level that the pressure difference between the vacuum inside the condenser and the atmospheric pressure is compensated by a liquid column. The height of this barometric leg must also overcome the flow resistance. In Figure 2.15, such a barometric installation is shown for a unit employing surface condensers. The height between the condensate outlet at the condenser and the liquid surface level in the collecting tank can be calculated by the necessary pressure difference and the specific weight of the... 

If there is not enough height available for a barometric installation, a pump has to be installed. Usually, such a pump is controlled by the hquid level above, so that there is always a liquid seal to prevent the inflow of air. Alternatively, a nonreturn valve must be mounted at the discharge side of the pump, but then cavitation has to be anticipated, if the drain pipe from the condenser is completely emptied by the pump. Collecting vessels are also used to collect the condensate under vacuum, discharging as required. For continuous operation, two or more alternating vessels are needed, and the ventilation and evacuation have to be considered. 

When several condensers with different pressures have to be drained, a semi-barometric installation is possible with a closed collecting tank instead of an open tank. In this tank, an interim vacuum exists, so that a given height is used and only one drain pump is needed. Such a system is illustrated in Figure 2.16. 

Figure 2.16 Semi-barometric installation with collecting tank and drain pump.

Pump Suction. The net positive suction head required (NPSHR) affects the resistance on the suction side of the pump. If it drops to or near the vapor pressure of the fluid being handled, cavitation and loss of performance occurs (13). The NPSHR is affected by temperature and barometric pressure and is of most concern on evaporator CIP units where high cleaning temperatures might be used. A centrifugal booster pump may be installed on a homogenizer or on the intake of a timing pump to prevent low suction pressures. 

As the altitude of an installation increases above sea level, the barometric pressure, and hence p or P decreases for any open vessel condition. This decreases the available NPSH. 

If the previous system were at sea level, consider the same pump with the same system at an altitude of 6000 feet. Here the barometric pressure is 27.4 feet of water. This is 34 — 27.4 = 6.6 feet less than the sea level installation. The new NPSHa will be 15 ft — 6.6 ft = 8.4 feet available. Referring to the pump curve of Figure 3-36A it is apparent that this pump cannot do greater than 21 feet suction lift as water or 12 feet NPSHr of liquid (fluid). 

Figures 6-5 and 6-6 illustrate two-stage ejector installations with barometric and surface t) pe inter-after condensers respectively. The discharge of the steam non-condensables from the second stage jet of Figure 6-5 is exhausted to the atmosphere, while in Figure 6-6 the steam is condensed in the aftercondenser and, essentially, only non-condensables leave the ent of the aftercondenser. Figure 6-7A indicates a diagram of a three-stage barometric type installation.

Installation arrangements, 351 Pump-down time, 380 Selection procedure, 374 Specification form, 377 Specifications, 373 Steam jet comparison, 356 Types of loads, 359 Ejectors, 346 Applications, 353 Barometric condenser, 249, 376 Booster, 370 Calculations Actual air capacity, 362 Air equivalent, 360... 

As many as six stages are represented on Figure 7.30, combined with interstage condensers in several ways. Barometric condensers are feasible only if the temperature of the water is below its bubblepoint at the prevailing pressure in a particular stage. Common practice requires the temperature to be about 5°F below the bubblepoint. Example 7.13 examines the feasibility of installing intercondensers in that process. 

A demister is sometimes installed at the top of the scmbber ahead of the vacuum unit, to reduce liquid carryover of small oil droplets, which would otherwise end up in the water from the barometric condenser or in the condensate from the cold (or dry) condensers. 

Differential pressure sensors are used to measure the bed pressure, leaving one leg open to the atmosphere to compensate for barometric pressure variations. Care must be taken in the installation to minimize the plugging with solids. This is normally done by tilting the tank nozzle on which the DP cell is mounted downward from the sensor, so the solids tend to settle away from the sensor surface. A shutoff valve and washer flush tap are recommended to allow easy maintenance. 

The column is made of carbon steel, but both packings are of stainless steel. The column will operate under vacuum with conditions of 55 kPa and bO C at the top and 60 kPa and 125°C at the bottom. A total of four liquid distributors or redistributors will be used. Estimate the f.o.b. purchase cost of the column, including installed packings, distributors, and redistributors, for a CE cost index of 410. The barometric pressure is 100 kPa. 

The filtrate recovered is separated by one filtrate receiver each from the hquid-gas mixture. The filtrate can either be discharged by a suitable pump or via a barometric leg. If vapour pressure, temperature and chemical properties of the slurry are such that the occurrence of undesirable vapours is likely, the use of a condenser is to be recommended. This is installed between separator and vacuum generator. 

As with centrifugal pumps, fans require stable inlet conditions. Ductwork should be configured to ensure an adequate volume of clean air or gas, stable inlet pressure, and laminar flow. If the supply air is extracted from the environment, it is subject to variations in moisture, dirt content, barometric pressure, and density. However, these variables should be controlled as much as possible. As a minimum, inlet filters should be installed to minimize the amount of dirt and moisture that enters the fan. 

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